Browsing by Author "Bai, Feiming"

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    An acoustic position sensor
    Dong, Shuxiang; Bai, Feiming; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2003-11-01)
    This article presents an acoustic method-the resonance acoustic field sensor or piezoelectric-sound-resonance cavity (PSRC)-for object position detection. This method utilizes the change of acoustic radiation impedance as a sensing mechanism. The PSRC both generates and detects a resonance acoustic field, along both the axial and transverse directions. We have discovered that an inserted object or an object motion in the sound radiation field results in changes in both the voltage and phase of the PSRC. Results have shown that a minimum object displacement of <10 mum can be detected in the axial direction (and <100 mum in the transverse) by this method. (C) 2003 American Institute of Physics.
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    Conformal sensor skin approach to the safety-monitoring of H-2 fuel tanks
    Dong, Shuxiang; Cao, Hu; Bai, Feiming; Yan, Li; Li, Jiefang; Viehland, Dwight D.; Gao, Y. K. (AIP Publishing, 2004-05-01)
    A conformal sensor skin approach has been developed for safety monitoring of H-2 fuel tanks. Small piezoelectrically driven sound resonance cavities were embedded in a porous polymer. When placed on a structural composite plate, it was found feasible to detect the leakage of small concentrations of H-2 in real time. (C) 2004 American Institute of Physics.
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    Correlation between structural deformation and magnetoelectric response in (1-x) Pb(Zr0.52Ti0.48)O-3-xNiFe(1.9)Mn(0.1)O(4) particulate composites
    Islam, Rashed Adnan; Jiang, Jiechao; Bai, Feiming; Viehland, Dwight D.; Priya, Shashank (AIP Publishing, 2007-10-01)
    The ferroelectric, ferromagnetic, and magnetoelectric properties of (1- x) Pb( Zr0.52Ti0.48)O-3 - xNiFe(1.9)Mn(0.1)O(4) (PZT- NFM) ceramic composites were found to be dependent upon postsinter annealing and aging. It was found on annealing and aging that (i) the size and density of the NFM phase is reduced, (ii) the PZT lattice constants changed from (a=3.8 angstrom, c= 4.07 angstrom) to (a= 4.07 angstrom, c= 4.09 angstrom), (iii) the ferroelectric and ferromagnetic Curie temperatures decreased by 8 and 33 degrees C, respectively, and (iv) the magnetoelectric coefficient increased by 50%. (C) 2007 American Institute of Physics.
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    Destruction of spin cycloid in (111)(c)-oriented BiFeO3 thin films by epitiaxial constraint: Enhanced polarization and release of latent magnetization
    Bai, Feiming; Wang, Junling; Wuttig, Manfred; Li, Jiefang; Wang, Naigang; Pyatakov, Alexander P.; Zvezdin, Anatoly Konstantinovich; Cross, L. E.; Viehland, Dwight D. (AIP Publishing, 2005-01-01)
    In BiFeO3 films, it has been found that epitaxial constraint results in the destruction of a space modulated spin structure. For (111)c films, relative to corresponding bulk crystals, it is shown (i) that the induced magnetization is enhanced at low applied fields; (ii) that the polarization is dramatically enhanced; whereas, (iii) the lattice structure for (111)(c) films and crystals is nearly identical. Our results evidence that eptiaxial constraint induces a transition between cycloidal and homogeneous anti ferromagnetic spin states, releasing a latent antiferromagnetic component locked within the cycloid. (C) 2005 American Institute of Physics.
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    Domain engineered states over various length scales in (001)-oriented Pb(Mg1/3Nb2/3)O-3-x%PbTiO3 crystals: Electrical history dependence of hierarchal domains
    Bai, Feiming; Li, Jiefang; Viehland, Dwight D. (American Institute of Physics, 2005-03-01)
    The dependence of the domain structure on poling for (001)-oriented Pb(Mg1/3Nb2/3)O-3-x%PbTiO3 crystals with x=20, 30, 35, and 40 has been investigated by scanning force microscopy in the piezoresponse mode and by polarized optical microscopy. The results demonstrate a domain hierarchy on various length scales, ranging from nanometers to millimeters, which is notably dependent upon the electrical history of the specimen. The results provide important insights into the nature of the domain engineered state in these crystals. (C) 2005 American Institute of Physics.
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    Domain hierarchy in annealed (001)-oriented Pb(Mg1/3Nb2/3)O-3-x%PbTiO3 single crystals
    Bai, Feiming; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2004-09-01)
    The domain structures of annealed (001)-oriented Pb(Mg1/3Nb2/3)O-3-x%PbTiO3(PMN-x%PT) crystals for x=10, 20, 30, 35, and 40 at.% have been investigated by polarized optical microscopy and scanning force microscopy in the piezoresponse mode. The results demonstrate the presence of a domain hierarchy on various length scales ranging from 40 nm to 0.1 mm, which varies with x. (C) 2004 American Institute of Physics.
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    Epitaxially induced high temperature (> 900 K) cubic-tetragonal structural phase transition in BaTiO3 thin films
    Bai, Feiming; Zheng, H. M.; Cao, Hu; Cross, L. E.; Ramesh, R.; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2004-11-01)
    For (001)(c) oriented BaTiO3 thin films, it has been found that epitaxial constraint can result in a dramatic increase in the temperature of a tetragonal (T) structural phase transition. For 2000-Angstrom-thick films grown directly on SrTiO3 substrates, a T-->cubic (C) phase transition was found on heating at >950 K, where the lattice constant changed smoothly with temperature. It was also found for films of the same thickness that the T-->C transition is nearly restored to that of bulk crystals by the use of a buffer layer, which relaxes the epitaxial constraint. These results provide evidence of an epitaxially induced high temperature structural phase transition in BaTiO3 thin films, where the ferroelectric (internal) and structural (external) aspects of the phase transition are decoupled. (C) 2004 American Institute of Physics.
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    Fe-Ga/Pb(Mg1/3Nb2/3)O-3-PbTiO3 magnetoelectric laminate composites
    Dong, Shuxiang; Zhai, Junyi; Wang, Naigang; Bai, Feiming; Li, Jiefang; Viehland, Dwight D.; Lograsso, Thomas A. (AIP Publishing, 2005-11-01)
    We have found large magnetoelectric (ME) effects in long-type laminate composites of Fe-20% Ga magnetostrictive alloys and piezoelectric Pb(Mg1/3Nb2/3)O-3-PbTiO3 single crystals. At lower frequencies, the ME voltage coefficient of a laminate with longitudinally magnetized and longitudinally polarized (i.e., L-L mode) layers was 1.41 V/Oe (or 1.01 V/cm Oe). Near the natural resonant frequency (similar to 91 kHz) of the laminate, the ME voltage coefficients were found to be dramatically increased to 50.7 V/Oe (36.2 V/cm Oe) for the L-L mode. In addition, the laminate can detect a minute magnetic field as low as similar to 2 x 10(-12) T at resonance frequency, and similar to 1 x 10(-10) T at lower frequencies. (c) 2005 American Institute of Physics.
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    Intermediate ferroelectric orthorhombic and monoclinic M-B phases in [110] electric-field-cooled Pb(Mg1/3Nb2/3)O-3-30%PbTiO3 crystals
    Cao, Hu; Bai, Feiming; Wang, Naigang; Li, Jiefang; Viehland, Dwight D.; Xu, Guangyong; Shirane, Gen (American Physical Society, 2005-08-01)
    Structural phase transformations of [110] electric-field-cooled Pb(Mg1/3Nb2/3)O-3-30%PbTiO3 (PMN-30%PT) crystals have been performed by x-ray diffraction. A phase sequence of cubic (C)-> tetragonal (T)-> orthorhombic (O)-> monoclinic (M-B) was found on field cooling (FC); and a rhombohedral (R)-> M-B-> O sequence was observed with increasing field, beginning from the zero-field-cooled condition at room temperature. The application of the [110] electric field induced a dramatic change in the phase sequence in the FC condition, compared to the corresponding data for PMN-30%PT crystals in a [001] field, which shows that the phase sequence in the FC condition is altered by the crystallographic direction along which a modest electric field (E) is applied. Only when E is applied along [110] are intermediate O and M-B phases observed.
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    Magnetic force microscopy investigation of domain structures in Fe-x at. % Ga single crystals (12 < x < 25)
    Bai, Feiming; Li, Jiefang; Viehland, Dwight D.; Wu, D.; Lograsso, Thomas A. (American Institute of Physics, 2005-07-15)
    The domain structure of furnace-cooled (FC) and post-annealed (PA) Fe-x at. % Ga (x=12, 20, and 25) crystals has been investigated by magnetic force microscopy. For both FC and PA Fe-12 at. % Ga, the domains were found to be well-aligned and oriented along the [100] direction. For Fe-20 at. % Ga, although a preferred [100] orientation remained, a difference in morphology was found between FC and PA conditions-in the PA condition, clear dendritic domains were observed. For both FC and PA Fe-25 at. % Ga, a much reduced [100] preferred domain orientation was found, the domain size was notably reduced, and dendrite formation was not observed. (c) 2005 American Institute of Physics.
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    Magnetic force microscopy investigation of the static magnetic domain structure and domain rotation in Fe-x at. %Ga alloys
    Bai, Feiming; Zhang, H. W.; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2009-10-01)
    Magnetic domain structures and domain rotation process in Fe-x at. %Ga (x=12, 19, and 25) alloys have been studied by magnetic force microscopy. Our results show that the missing connection between magnetic domains and the underlying microstructure [Xing and Lograsso, Appl. Phys. Lett. 93, 182501 (2008)] is (i) a perpendicular magnetic anisotropy; and (ii) domain irregularities/fluctuations induced by a quenched random-field condition: both of which may have direct relations with dispersed low-symmetry nanoprecipitates [Cao, et al., Phys. Rev. Lett. 102, 127201 (2009)]. (C) 2009 American Institute of Physics. [doi:10.1063/1.3238062]
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    Magnetostrictive and magnetoelectric behavior of Fe-20 at. % Ga/Pb(Zr,Ti)O-3 laminates
    Dong, Shuxiang; Zhai, Junyi; Bai, Feiming; Li, Jiefang; Viehland, Dwight D.; Lograsso, Thomas A. (American Institute of Physics, 2005-05-15)
    The magnetostrictive and magnetoelectric (ME) properties of laminate composites of Fe-20 at. % Ga and Pb(Zr,Ti)O-3 (PZT) have been studied for laminates of different geometries. The results show that (i) a long-type magnetostrictive Fe-20 at. % Ga crystal plate oriented along (001), and magnetized in its longitudinal (or length) direction has higher magnetostriction than a disk-type one; and consequently (ii) a long-type Fe-20 at. % Ga/PZT laminate has a giant ME effect, and is sensitive to low-level magnetic fields. (c) 2005 American Institute of Physics.
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    Polarization switching in (001)-oriented Pb(Mg1/3Nb2/3)O-3-x%PbTiO3 crystals: Direct observation of heterogeneous nucleation by piezoreponse force microscopy
    Bai, Feiming; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2004-11-01)
    Polarization switching in (001)-oriented Pb(Mg1/3Nb2/3)O-3-x%PbTiO3, PMN-x%PT, crystals for x=20 and 35 has been investigated in situ by scanning force microscopy in a piezoresponse mode, under a step-increased dc electrical voltage (V-dc). The results demonstrate that switching initiates by the nucleation of nanosized polar regions with a reversed polarization. For x=20, nucleation occurs heterogeneously throughout the volume of the crystal. However, with increasing PT content, nucleation tends to preferentially initiate near preexisting twin boundaries; with increasing V-dc, the domains becoming increasingly "diffuse" due to heterogeneous nucleation and growth throughout the crystal. (C) 2004 American Institute of Physics.
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    Push-pull mode magnetostrictive/piezoelectric laminate composite with an enhanced magnetoelectric voltage coefficient
    Dong, Shuxiang; Zhai, Junyi; Bai, Feiming; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2005-08-01)
    A magnetoelectric (ME) laminate composite consisting of a symmetric longitudinally poled piezoelectric Pb(Mg1/3Nb2/3)O-3-PbTiO3 crystal and two longitudinally magnetized magnetostrictive Tb1-xDyxFe2 layers has been developed that has a notably superior ME voltage coefficient, relative to previous laminate configurations. The symmetric nature of the longitudinally poled piezoelectric layer allows for operation in a push-pull mode that optimizes elastic coupling between layers. Our small laminate has a giant ME voltage coefficient of similar to 1.6 V/Oe at low frequencies, a significant enhancement of this coefficient to similar to 20 V/Oe under resonance drive, and an exceptional low-level magnetic field sensitivity of similar to 10(-12) T at f=f(0). (c) 2005 American Institute of Physics.
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    Resonance acoustic field position sensor
    Dong, Shuxiang; Bai, Feiming; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2003-06-01)
    An acoustic position sensor, based on a piezoelectric-sound-resonance cavity (PSRC), is reported in which a resonance acoustic field is used as the sensing mechanism. It has been discovered that an inserted object or an object motion in the sound radiation field results in changes in the resonance state of the PSRC. Experiments have demonstrated a high position resolution in the axial direction, and also good sensitivity in the transverse. (C) 2003 American Institute of Physics.
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    Sound-resonance hydrogen sensor
    Dong, Shuxiang; Bai, Feiming; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2003-06-01)
    A hydrogen sensor is reported in which a small piezoelectric-sound-resonance-cavity (PSRC) is used as the sensing element. Detection utilizes sound resonance and acoustic property differences between H-2 and air as a sensing mechanism. Changes in H-2 concentration result in a shift of the sound-resonance state of the PSRC. Preliminary experiments have demonstrated a sensitivity limit of 8 ppm, a fast response time similar to1.5 second, and detection capabilities over a broad concentration range 10(-5) < n < 0.2. (C) 2003 American Institute of Physics.
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    Structural phase transformation and phase boundary/stability studies of field-cooled Pb(Mg1/3Nb2/3O3)-32%PbTiO3 crystals
    Cao, Hu; Bai, Feiming; Li, Jiefang; Viehland, Dwight D.; Xu, Guangyong; Hiraka, Haruhiro; Shirane, Gen (American Institute of Physics, 2005-05-01)
    Structural phase transformations in (001)-oriented (1-x)Pb(Mg1/3Nb2/3O3)-32%PbTiO3 crystals have been investigated by x-ray diffraction. A C -> T -> M-C sequence was observed in both the field-cooled and zero-field-cooled conditions. Most interestingly, an anomalous increase in the C -> T phase boundary with increasing field has been observed, which is seemingly a common characteristic of crystals whose compositions are in the vicinity of the morphotropic phase boundary, irrespective of the width of the T and M-C phase regions. (C) 2005 American Institute of Physics.
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    Structure-Property Relationships of Multifeorric Materials: A Nano Perspective
    Bai, Feiming (Virginia Tech, 2006-04-28)
    The integration of sensors, actuators, and control systems is an ongoing process in a wide range of applications covering automotive, medical, military, and consumer electronic markets. Four major families of ceramic and metallic actuators are under development: piezoelectrics, electrostrictors, magnetostrictors, and shape-memory alloys. All of these materials undergo at least two phase transformations with coupled thermodynamic order parameters. These transformations lead to complex domain wall behaviors, which are driven by electric fields (ferroelectrics), magnetic fields (ferromagnetics), or mechanical stress (ferroelastics) as they transform from nonferroic to ferroic states, contributing to the sensing and actuating capabilities. This research focuses on two multiferroic crystals, Pb(Mg1/3Nb2/3)O3-PbTiO3 and Fe-Ga, which are characterized by the co-existence and coupling of ferroelectric polarization and ferroelastic strain, or ferro-magnetization and ferroelastic strain. These materials break the conventional boundary between piezoelectric and electrostrictors, or magnetostrictors and shape-memory alloys. Upon applying field or in a poled condition, they yield not only a large strain but also a large strain over field ratio, which is desired and much benefits for advanced actuator and sensor applications. In this thesis, particular attention has been given to understand the structure-property relationships of these two types of materials from atomic to the nano/macro scale. X-ray and neutron diffraction were used to obtain the lattice structure and phase transformation characteristics. Piezoresponse and magnetic force microscopy were performed to establish the dependence of domain configurations on composition, thermal history and applied fields. It has been found that polar nano regions (PNRs) make significant contributions to the enhanced electromechanical properties of PMN-x%PT crystals via assisting intermediate phase transformation. With increasing PT concentration, an evolution of PNRï  PND (polar nano domains)-> micron-domains-> macro-domains was found. In addition, a domain hierarchy was observed for the compositions near a morphotropic phase boundary (MPB) on various length scales ranging from nanometer to millimeter. The existence of a domain hierarchy down to the nm scale fulfills the requirement of low domain wall energy, which is necessary for polarization rotation. Thus, upon applying an E-field along <001> direction(s) in a composition near the MPB, low symmetry phase transitions (monoclinic or orthorhombic) can easily be induced. For PMN-30%PT, a complete E-T (electric field vs temperature) diagram has been established. As for Fe-x at.% Ga alloys, short-range Ga-pairs serve as both magnetic and magnetoelastic defects, coupling magnetic domains with bulk elastic strain, and contributing to enhanced magnetostriction. Such short-range ordering was evidenced by a clear 2theta peak broadening on neutron scattering profiles near A2-DO3 phase boundary. In addition, a strong degree of preferred [100] orientation was found in the magnetic domains of Fe-12 at.%Ga and Fe-20 at.%Ga alloys with the A2 or A2+DO3 structures, which clearly indicates a deviation from cubic symmetry; however, no domain alignment was found in Fe-25 at.%Ga with the DO3 structure. Furthermore, an increasing degree of domain fluctuations was found during magnetization rotation, which may be related to short-range Ga-pairs cluster with a large local anisotropy constant, due to a lower-symmetry structure.
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    Vacuum response and gas leak detection in piezoelectrically driven sound-resonance cavity
    Dong, Shuxiang; Bai, Feiming; Yan, Li; Cao, Hu; Li, Jiefang; Viehland, Dwight D. (AIP Publishing, 2004-05-01)
    It has been found that a piezoelectrically driven sound-resonance cavity (PSRC) is quite sensitive to low-pressure changes: a change from ambient to vacuum (67 Pa) conditions results in a 89degrees phase shift and a -81% voltage decrease. Under vacuum conditions, the PSRC is highly sensitive (similar to7 ppm) to leakage of H-2 gas. (C) 2004 American Institute of Physics.
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    X-ray and neutron diffraction investigations of the structural phase transformation sequence under electric field in 0.7Pb(Mg1/3Nb2/3)-0.3PbTiO(3) crystal
    Bai, Feiming; Wang, Naigang; Li, Jiefang; Viehland, Dwight D.; Gehring, Peter M.; Xu, Guangyong; Shirane, Gen (American Institute of Physics, 2004-08-01)
    The structural phase transformations of 0.7Pb(Mg1/3Nb2/3)O-3-0.3PbTiO(3) (PMN-30%PT) have been studied using x-ray diffraction (XRD) and neutron scattering as a function of temperature and electric field. We observe the phase transformational sequence (i) cubic (C)--> tetragonal (T)--> rhombohedral (R) in the zero-field-cooled (ZFC) condition; (ii) C-->T--> monoclinic (M-C)--> monoclinic (M-A) in the field-cooled (FC) condition; and (iii) R-->M-A-->M-C-->T with increasing field at fixed temperature beginning from the ZFC condition. Upon removal of the field, the M-A phase is stable at room temperature in the FC condition, and also in the ZFC condition with increasing field. Several subtleties of our findings are discussed based on results from thermal expansion and dielectric measurements, including (i) the stability of the M-A phase, (ii) a difference in lattice parameters between inside bulk and outside layer regions, and (iii) a difference in the phase transition temperature between XRD and dielectric data. (C) 2004 American Institute of Physics.